The present invention relates to pressure-sensitive adhesive container or can sealing tapes, particularly to such tapes which are adapted to be die-cut and applied as peel-open tabs over corresponding holes die-cut in the tops of juice cans, for example. Such tapes have been proposed with backings of metal foil or metallized polyester film and the latter has achieved substantial commercial acceptance.
Metallized polyester film backed pressure-sensitive adhesive tapes have been used for a number of years for sealing die-cut holes in the tops of juice cans as indicated above. Tape of this type currently being supplied to can manufacturers consists of the following components: a 2-mil thick polyester film, a layer of metallization vacuum deposited on one of the major surfaces of the polyester film, a protective coating applied over the metallization to protect the metallization from oxidation or corrosion by acid, a pressure-sensitive adhesive layer applied over a thin primer coating anchoring the adhesive to the other major surface of the polyester film, and a silicone-coated paper release liner applied to the free surface of the adhesive to allow the tape to be wound into a roll. This release liner is removed from the tape structure just as it is introduced to a die cutting machine which sequentially cuts the tab and applies it properly-positioned to the die-cut hole in the can lid.
This tape structure requires a multitude of steps in its production, is difficult to make, and is subject to high waste. After metallization, the polyester film must be primed on one side and then the protective coating must be applied over the metallization on the other side of the film. The adhesive is coated on the silicone liner, dried and then laminated to the primed surface of the polyester backing film. The bond between the primer and the adhesive does not develop immediately and the tape must be stored a month or two in order to provide a good bond between adhesive and primer. Finally, the liner must be removed to allow the tape to be used, and then it must be disposed of. This type of tape is described in U.S. Pat. No. 3,389.827.
Past efforts to provide a linerless tape have been fraught with many problems and disappointments. It has been impossible to produce a product with a consistently good release and barrier coating over the metallization. The metallization has a tendency to pick-off and thereby delaminate, particularly when a heavy metallized layer is applied.